Turbine blades are those elements of wind turbines that serve to catch wind for then converting wind energy into electrical energy. A plurality of blades may be connected to the rotor. The working principle of the blades is similar to that of an airplane wing. The blades may have a varying cross-sectional profile of different airfoils along its length. The airfoil profile shape ensures that, during operation, air that flows over the blade produces a pressure difference between a suction side and a pressure side. Consequently, an aerodynamic force is exerted on the turbine blades.
A component of this aerodynamic force is the lift force, which is directed “upwards” (i.e. this force is directed from the pressure side towards the suction side). The lift force generates torque on the main rotor shaft, which. The rotation of the rotor shaft drives the generator rotor either directly (“direct driven”) or through the use of a gearbox. The generator produces the electricity which may be fed into an electrical grid.
The lift force mentioned before is generated when the flow from the leading edge to the trailing edge creates a pressure difference between the top and bottom surfaces of the blade. Depending on the angle of attack the aerodynamic flow may be attached along the top surface (suction side) from the leading edge almost to the trailing edge.
The aerodynamic force exerted on the wind turbine blades as a result of the pressure difference between the pressure side and the suction side caused by an air flow may be counterproductive during manipulation (i.e. installation, transport, storage, etc.) of the wind turbine blades. For example, during installation of the wind turbine blade on a wind turbine rotor that is assumed to be already at its location on top of the tower. The afore-mentioned aerodynamic force exerted on the blade may provoke the oscillation of the blade during the hoisting of the blade. Thus, difficulties during the installation may arise, i.e. a lack of safety, possible damage to the blade or to any other part of the wind turbine, time delays during the installation process, etc. This may be even more problematic in offshore wind parks where the wind speeds are considerably higher than in onshore wind parks and they may exceed a predetermined maximum value at which it may not be possible to install the wind turbine blade, overall, when said blade is installed in a substantially vertical manner. This fact may provoke a considerable delay in the installation of the wind turbine blade and an increase of the costs.
In examples of the present invention, the afore-mentioned problems may be at least partially solved.